1. Field of Invention
The present invention relates to electrochromic display devices and more particularly to electrochromic display devices consisting of a plurality of segments which are selectively driven to display various patterns.
2. Prior Art
Image display devices using materials which produce coloration as a result of electrochemical oxidation reduction processes, such as electrochromic materials, are well known in the art. Display devices using inorganic oxides, such as, for example, tungsten oxide, molybdenum oxide and the like, as electrochromic material, are disclosed, for example, in U.S. Pat. No. 3,827,784. Display devices using organic dies such as, for example, viologen, are disclosed in U.S. Pat. No. 3,806,229. These electrochromic display devices require more electrical energy in order to produce or erase coloration than that required for driving liquid crystal display devices. However, once an image is displayed, it is maintained without further energy consumption because electrochromic display devices possess memory action. Thus, their average energy consumption is about equal to that required in driving liquid crystal display devices. Moreover, good legibility is obtained in the electrochromic display device since display contrast does not rely on visual angles. The electrochromic display device, therefore, is a suitable display device for electronic timepieces, calculators and the like. Electronic timepieces using electrochromic display devices are disclosed in U.S. Pat. Nos. 3,839,857 and 3,950,936. Such electronic timepieces display numbers by selectively driving display electrodes made up of a plurality of segments so as to produce coloration in a selected combination of segments.
Because coloration in electrochromic display devices is an electrochemical reaction, color density is proportional to the quantity of electricity flowing in the display electrode per square area. Thus, if many segments are driven simultaneously at a specified voltage for a specified period of time, each segment would have a different color density depending on the size of the segment and/or the number of segments that are driven simultaneously. Such a result would greatly impair the legibility of the display.